The resistor for 85-20V is a bad idea for more reasons than heat alone: if your current draw is not 70 mA but just 10 mA (it will vary that much depending on which components are active) your 65V drop becomes a 9V drop, and you may fry your linear regulator. On the other hand the resistor will be too large to handle even a 200 mA peak.
What you need is a buck converter, not a linear converter. Otherwise there's the power issue as pointed out above. They indeed can get quite small. A quick search turned up this little guy takes up to 55V on the input, and produces 5V on the output.